As a general rule if it is a temperature you would be happy with then the worms will be happy. The planters greenery would have to be massively lush to block the sun from the top and sides. One could go broke just paying for all those tiny umbrellas in their drink requests. I think it would work great until that one really sunny day where it would not work. In an old compost heap that touches the ground one hopes the worms dive out of the heat. A serious investment in worms might prefer shade.

Just one bad day........ I get your drift. Most Self watering containers use a 'mix' rather than soil, as the soil gets too commpact. With earthworms in the mix, I hope to use a more natural soil in the containers. I figure a handfull of worms from their bin into the container and fed scraps or manure in a special spot would supply worms to aerate the container. I can just replinish them after a heat wave the same way, but i don't want to torture such good little helpmates.

I learned the answer to your question the hard way. My worms were in shade on a screened in porch. They were fed appropriately, dampened daily if the top layer of bedding dried out, and I did everything as ordered in the forums.

They didn't make it. The heat (think climate change unalleviated drought and heat) in Missouri had them clump together until they crawled off to die, one by one.

Now I have them in the basement, with just a partial handful of survivors. I've read of bins surviving the heat. But it hasn't been my experience.

Best of luck.

Yes, I'd avoid using any container exposed to direct sun. Mine are in an outdoor closet on the shady side of the house, and I check temperatures twice a day when it's hot.

Heat is the most acute threat to worms, partly because microbial action keeps compost warmer than ambient air, partly because, as folks above note, it just takes one hot afternoon to do them in. Freezing cold or dryness will kill them too, but not nearly so fast.

Poor worms:-(